1. Field of Invention
The invention relates to a variable valve mechanism for an engine provided with a maximum valve lift amount variable mechanism that changes a maximum valve lift amount of an engine valve (at least one of an intake valve and an exhaust valve), and a valve timing variable mechanism that changes a valve operation timing (valve timing).
2. Description of Related Art
A publication of Japanese Patent Application Laid-Open No. 2001-263015 discloses a known maximum valve lift amount variable mechanism for changing a maximum valve lift amount of an engine valve, which includes a control shaft that is movable in an axial direction, and a plurality of valve lift mechanisms provided thereon for changing the maximum valve lift amount of the engine valve.
In the aforementioned maximum valve lift amount variable mechanism, the control shaft is moved in the axial direction such that a relative phase difference between an input arm and an output arm provided in the valve lift mechanism is changed for adjusting the maximum valve lift amount of the engine valve.
Another publication of Japanese Patent Application Laid-Open No. 11-324740 discloses a known variable valve timing mechanism for changing a valve timing of an engine valve, which includes a vane rotor that can be rotated together with a cam shaft of the engine, and a housing that can be rotated together with a pulley or a sprocket of the engine such that an advance pressure chamber and a retardation pressure chamber are defined by the vane rotor and the housing.
In the above-structured variable valve timing mechanism, the amount of oil supplied to the respective pressure chambers is adjusted to change the rotary phase of the cam shaft relative to that of the crankshaft for changing the valve timing of the engine valve.
The variable valve mechanism provided with the maximum valve lift amount variable mechanism and the variable valve timing mechanism makes it possible to control the valve characteristics with a higher degree of freedom in accordance with an engine operation state.
Another publication of Japanese Patent Application Laid-Open No. 2000-328911 discloses a known variable valve mechanism provided with a maximum valve lift amount variable mechanism that changes the maximum valve lift amount of the engine valve by changing a cam among a plurality of cams each having a different lift amount.
The engine provided with the aforementioned variable valve mechanism may cause the piston to be in contact with the engine valve when the maximum valve lift amount or the valve timing is changed. For example, when the valve timing of the intake valve in the state where the advance angle is set to X1, and the maximum valve lift amount is set to Y is advanced to the advance angle X2, the piston is brought into contact with the intake valve.
The variable valve mechanism provided with the maximum valve lift amount variable mechanism and the variable valve timing mechanism is required to avoid the contact between the piston and the engine valve as aforementioned.
In the publication of Japanese Patent Application Laid-Open No. 2000-328911, when the cam with a large lift amount is selected, a pin that limits the advance angle of the valve timing variable mechanism is operated by a work fluid of the maximum valve lift amount variable mechanism so as to avoid the contact between the piston and the engine valve.
However, this system can not be applied to other variable valve mechanisms such as the one disclosed in Japanese Patent Application Laid-Open No. 2001-263015 due to the fundamental difference in the structure of this maximum valve lift amount variable mechanism.